MOLONEY MURINE LEUKEMIA-VIRUS ENVELOPE PROTEIN SUBUNITS, GP70 AND PR15E, FORM A STABLE DISULFIDE-LINKED COMPLEX

The nature and stability of the interactions between the gp70 and Pr15 E/p15E molecules of murine leukemia virus (MLV) have been disputed ext ensively. To resolve this controversy, we have: performed quantitative biochemical analyses on gp70-Pr15E complexes formed after independent expression of the amphotropic and ecotropic Moloney MLV env genes in BHK-21 cells. We found that all cell-associated gp70 molecules are dis ulfide linked to Pr15E whereas only a small amount of free gp70 is rel eased by the cells. The complexes were resistant to treatment with red ucing agents in vivo, indicating that the presence and stability of th e disulfide interaction between gp70 and Pr15E are not dependent on th e cellular redox state. However, disulfide-bonded Env complexes were d isrupted in lysates of nonalkylated cells in a time-, temperature-, an d PB-dependent fashion. Disruption seemed not to be caused by a cellul ar factor but is probably due to a thiol-disulfide exchange reaction o ccurring within the Env complex after solubilization. The possibility that alkylating agents induce the formation of the intersubunit disulf ide linkage was excluded by showing that disulfide-linked gp70-Pr15E c omplexes exist in freshly made lysates of nonalkylated cells and that disruption of the complexes can be prevented by lowering the pH. Toget her, these data establish that gp70 and Pr15E form a stable disulfide- linked complex in vivo.